The data below is from an experiment in which transgenic mice were created with polymerase mutations that allow normal DNA polymerase activity but have inactive proofreading ability (i.e. 3' exonuclease activity). The longevity (top figure) and tissue tumor incidence (bottom figure) for the mutant Polymerase epsilon (Pole e/e), Polymerase delta (Pol d1 e/e) and mutation in both (Pol e/Pol d)are shown. Explain why these defects would lead to increased tumor formation. Why do you think there are tissue type differences in the accumulation of tumors in these mutant mice (Limit 5-6 sentences)?

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